Article of magnesium-base alloy and method of making



United States Patent Ofilice 3,119,684 Patented Jan. 28, 1964 3 119 684 ARTIQLE or MAGNESIlJM-BASE ALLOY AND warrior) or MAKING George S. Foerster, Midland, Mich., assignor to The Dow appreciably decreased by exposure of the alloy to elevated temperatures.

These and other objects and advantages of the invention will be more fully understood on becoming familiar with 5 the following description and the appended claims. ggffig: Company Mldland Mich" corpomhon of This invention is predicated on the discovery that, by No Drawing. Filed Nov.27, 1961, Ser. No. 155,164 Preparmg mgnesmm'hase alloy F' magrlestum 7 Claims. (CL 75-05) and one or more constituents which are each miscible with magnesium in the molten state but substantially 1n- The invention relates to die-expressed articles of mag- 10 301111116 solldlfied magneslum and y rapid solldlficatlofl nesium-base alloy. It more particularly concerns an im- 0f S181d l y for mp Into a ma S$ atomized P proved method of producing die-expressed articles of dishefltlng, cqmpactmg and l p f t0 q W310 hardened magnesium base alloys whereby good an ext-rude or die-expressedarticle, the so-obtained article mechanical properties are attained which are not appreexhibits exoeptionally deslrable mechanical P P E ciably lowered by exposure to elevated temperatures. For 4116 P P 0f the p fi t f and pp clams This application is a cominuaptiommyart f a i the term solidified magnesium is to be understood to filed application, Serial No. 810,257, filed May 1, 1959, Include solidlfied magqeswm-base ynow abandoned. In carrylng out the invention, a magneslunr-base alloy Heretofore high strength magnesium-base alloys have contaimflg j Paw/em of magnesium prePafsd been prepared by alloyinlg magnesium with one or more by alloying, aficol'dlng We11 known methods, g suitable constituents which are capable of forming solid and 0m more coflstltuems s the heriimafisr solutions with magnesium. Such alloys are often further finfid p fi P P A11 65561111211 P must treated, as by cold-working, to increase yield and tensile have Sufiiqwnt solllblllty 111 molten magnesium at i strength. However, at elevated temperatures the eifectiveable anolymg PP 'f example to ness of solid solution strengthening is limited and further but so'hd solub'l'hty m m i m less than 9- atomic the benefits of cold-working are soon lost because recovery PEYCQTIL AS tO the 301K! solublllty -1I1 Inag116S1uIX 1, those and recrystallization to a coarser grained condition takes filemems whlch 0I1 00l1ng 'f an Q- m place upon heating the alloys to even rather moderate Pound W magmas/mm and f are msqhl'ble Sohd temperatures. In other attempts to produce high strength magnesium are P Y The lflsoluble P l F magnesium-base alloys having a fine grained crystal suspenflied the rapidly cooled and sohdlfymg structure, fi magnesium powder having a thin Oxide nesium. It 1s furth er desired that the molten alloyhave coating has been die-expressed to produce an extrude in a nan-9w mhdlficatlon Z F i i S126 ofihe micr- Which magnesium oxide is Widely and finely dispersed meta'nlc y i 1S i i It ls.deslred in a magnesium metal mam), While Soiormed extrudes that the mtermetalhc particles dispersed in the solid magexhibit good mechanical properties, they tend to be quite i z i g g gg i g gfi i g ggfi f z b%g 32 12; brittle and i f to form even at elefiated tempers?- since the smaller particle size, the more the improvement tures; In i extremfaly fine P powder 15 in properties that results. A few particles having larger a e to Provide sufiiclenily f dlsperslon of the diameters can be tolerated, but they should he kept to X1de i extrude as Pxlde 15 P t y as a 511T 40 a minimum to avoid adversely affecting the properties of face coaflng On the 'l metal P Th3 the final product. Suitable metal constituents that may Prepafailon 0f magnfilum P of Sufficlent fineness be used singly or in combination in the practice of the for use in the aforesaid method is not only expensive but i ntion include barium, cobalt, copper, germanium, anthe fine powder is dangerous to handle because it forms timony, nickel, silicon and strontium, the pertinent properexplosive mixtures with air. ties of which are listed in Table I.

TABLE I Liquid Solidus Inter- Wt. percent Solubility Solubility Temperametallic of Constituent Alloying in Mg, in Mg at ture of Compound to Form 10% Constituent Wt. percent 800 0., Mg Binary, Formed by Volume of Wt. percent C. With Mg Intermetallic Compound 0.08 ca.100 634 Mg Ba ca. 5. nil ca. 12 633 Mg Oo. ca. 8. nil ca. 25 635 Mg2Ge. ca. 10. 0. 02 021.50 629 Mg Sbz 021.18. 0. 003 4 638 Mgtsinn. ca. 13. 0.01 582 Mg srmu ca. 3.

The alloy to be used is brought to the molten state in any convenient manner in preparation for rapid solidification. Temperatures in the order of 25 to 50 centigrade degrees above the melting point of the alloy are desirable although other temperatures may be used at which the alloy is in the molten state. It is preferable to use the lower temperature of a molten state not only so as to reduce the degree of hazard involved in handling the molten alloy but also to reduce the amount of heat which must be removed to permit the molten alloy to return to the solid state. It is highly desirable for reasons hereinafter more fully discussed that the solidification of the a,119,es4

'2 u atomized alloy take place quickly in order to minimize aggregation or crystal growth of intermetallic compounds which are insoluble in magnesium in the solid phase.

The alloy while in the molten state may be subjected to a dispersion and chilling operation whereby the metal is obtained in atomized. form, that is in the form of fine individually frozen discrete pellets. There are various ways in which atomization may be performed and any one of them may be used. A convenient method appears to be directing a jet of an inert cooling gas against an unconfined stream of the molten alloy as described in US. Patent No. 2,630,623.

For example, a freely falling stream of the molten alloy may be broken into droplets and solidified by impinging upon the stream an inert gas such as a hydrocarbon gas (e.g., methane, natural gas, ethane, propane, butane, etc.), argon, helium, hydrogen, the inert gas having a boiling temperature below the melting point of the molten metal. A wide range of pellet sizes, although small, usually results from the atomizing operation. The atomized product comprises more or less spherical pellets for the most part ranging in size from about mesh to smaller than 325 mesh. A preferred range of pellet sizes is from about -325 to about 140 mesh because of the outstanding properties achieved. However, very good properties are achieved with pellet sizes predominating in the 30 to 60 mesh range.

These pellets exhibit very desirable mechanical properties and may be used as pellets per se, for example, to reinforce other metals, as a load support, etc. or may be further fabricated, as by extrusion, rolling and the like.

Of course, other methods of rapidly quenching appropriate alloy compositions, as well as other methods of atomizing magnesium may be employed.

As a result of the atomizing operation, there is imparted to each pellet of the magnesium-base alloy a special heterogeneous microstructure essential in achieving the objects of this invention. This structure is characterized by a magnesium metal matrix having uniformly dispersed therethrough a discontinuous phase made up of very fine crystallites of an insoluble intermetallic com- It has been found that the as-atomized magnesium-base alloy may be heated in bulk to the desired temperature merely by placing it in a suitable metal vessel in a heated oven. Or, it is possible to charge the heated container of a die-expressing apparatus, with as-atomized metal and proceed with the operation of the apparatus to effect dieexpression with substantially no destruction of the asatomized structure of the alloy.

The amount of reduction in the cross-sectional dimensions of the compact effected bythe extrusion or dieexpression is subject to wide variations and may be from about 5 to 1 to as much as 200 to 1 or more (i.e., from about 80 percent to over 99 percent reduction in crosssectional area).

The so-produced extrude having a uniform dispersion of finely divided intermetallic compound exhibits enhanced properties at both room temperature and elevated temperatures and is less adversely affected by fabrication or heat treatment at high temperatures.

Example In accordance with the present invention, a quantity of each of four magnesium-base alloys in atomized form was provided. The compositions of these alloys are listed in Table II for runs No. 1, 2, 3 and 4. In each instance, the atomized pellets contained a uniform dispersion of intermetallic compound in which the intermetallic compound had an average diameter of about 0.00005 inch, substantially none of the intermetallic compound having a diameter greater than 0.0001 inch. In each case the quantity of atomized material was charged into a cylindrical container 3 inches in internal diameter, the container being at 400 C. The charge had a depth of about 6 inches and was compacted at 400 C. in the container to a compact about 4 inches long. The compact was then die-expressed at the same temperature at a rate of 5 feet per minute into a strip having a rectangular cross section 1% inches by inch, the reduction in area being about 90:1. The so obtained die-expressed articles were subjected to physical testing at 24 C., 315 C. and 427 C. The results of the tests are listed in Table II.

Table I1 Composition 1 Properties at 24 0. Properties at 316 0. Properties at 427 0.

Run No.

Per- Per- Per- Per- Per- Per- Percent cent cent cent cent TYS CYS TS cent TYS TS cent TYS TS Si Ba Zn Z E E E 4.5 4 46 35 53 23 4.0 7.1 44 1 d 2.2 8. 3 1 51 48 54 28 4. 4 7. 4 35 1 6 2. 5 5 30 24 5.3 8.2 23 2 2 3.6 6 0. 5 15 40 40 50 ca 100 1.0 2.0 inttinil nil 1 Balance magnesium.

pound. The intermetallic compound is present in an amount by volume from about 0.5 to 20 percent. A more preferred range is from about 3 to 15 percent of the volume of the alloy.

In the next step of the method the atomized metal is heated in preparation for compacting and die-expression. Compacting and die-expression may be carried out in conventional apparatus designed for the extrusion of magnesium-base alloy. A suitable method and apparatus for carrying out the die-expression of pelletized magnesium is described in U.S. Patent No. 2,630,623. The temperature to which the metal is heated is within the conventional plastic deformation temperature ranges for magnesium-base alloys, usually between about 300 and 500 C. but always below that temperature which adversely affects the dispersion through agglomeration.

By way of comparison the atomized form of a conventional alloy, having the AS'IM designation ZK 60 and a nominal composition of 6 weight percent of zinc, 0.5 weight percent of zirconium (thus, essentially no insoluble intermetallic compound), the balance magnesium, was similarly charged into the same heated die-expression apparatus and similarly extruded into 1%. inches by inch strip. The so-obtained strip was subjected to physical testing at 24 C., 315 C. and 427 C. The results of this comparison test are listed in Table H as run No. 5.

To further show the advantages of the process of the present invention, using a uniform dispersion of fine particles of intennetallic compound (in this instance Mg- Si), in contrast to large particles of intermetallic compound, pellets and ingots were extruded at 5 feet per minute in the same manner above described and the properties of the resulting extrude determined. These results are summarized in Table III.

TABLE III Per- Per- Percent cent Form Size cent TYS OYS TS Si Zn 1. 4 1. Ingot 0005 24 16 37 1.4 1.0 Pellet (35/65 .00005 3 4.3 36 50 mesh). 1. 4 1. 0 Pellet (-100 .00001 3 47 41 54 mesh).

1 Size of uniformly dispersed Mg Si iutermetallie compound in inches In another embodiment of the invention, a magnesiumbase alloy is prepared by making suitable additions to magnesium of a metal constituent, which forms an insoluble phase therewith as described hereinabove as well as one or more metals which increase the strength of magnesium in a Well known conventional manner such as by solution and precipitation hardening. It has thus been found that the benefits of dispersion hardening may be combined with the bene fits of increasing the strength of the matrix about the finely dispersed crystallites of solid insoluble phase. Further, the problem of grain refining magnesium alloys is largely eliminated. This is especially important in the case of alloys of magnesium With manganese Which tend to crystallize in a coarse grain structure, but in the fine grained condition exhibit excellent physical properties. Metals which may be added variously to increase the matrix strength include:

Rare earth metals 0-2 Combinations of the above listed elements which are mutually insoluble in molten magnesium to the extent that they form precipitates which settle out of the melt include AlTl1, AlZr, and Mn-Zr. It is the skill of the metallurgist to check desired combinations for mutual insolubility. In general, any conventional magnesium-base alloy system may be employed, such as Mg- Al, MgZn, MgAlZn, MgZnZr, or Mg-Al Mn, in combination With one or more of the previously mentioned metals which form a solid insoluble phase in solidified magnesium.

Such composite alloys, that is, those including dispersion hardening as well as conventional strengthening alloying metals, are atomized, compacted and extruded as described above.

Various modifications may be made in the present invention without departing from the spirit or scope thereof, and it is to be understood that 1 limit myself only as defined in the appended claims.

What is claimed is:

1. Atomized pellets comprising from 0.5 to by volume of solid insoluble particles of magnesium intermetallic compound and the balance magnesium-base alloy; said particles of magnesium intermetallic compound being intimately and uniformly dispersed throughout said magnesium-base alloy; said particles oi magnesium intermetallic compound having a maximum diameter of 0.0001 inch; said magnesium inter-metallic compound being formed of magnesium and a constituent, said constituent having a solid solubility in magnesium of less than 0.1 atomic percent; said atomized pellets comprising at least 70% of magnesium; and said atomized pellets having diameters smaller than about 10 mesh.

2. Atomized pellets comprising from 0.5 to 20% by volume of solid insoluble particles of magnesium intermetallic compound and the balance magnesium-base allo said particles of magnesium intermetallic compound being intimately and uniformly dispersed throughout said magnesium-base alloy; said particles of magnesium intermetallic compound having :a maximum diameter of 0.0001 inch; said magnesium intermetallic compound being formed by magnesium With an element selected from the group consisting of barium, cobalt, copper, germanium, antimony, nickel, silicon, strontium and mixtures thereof; and said atomized pellets having diameters smaller than about 10 mesh.

3. Atomized pellets as in claim 2 comprising from 3 to 15% by volume of solid insoluble particles of magnesium intermetallic compound having a maximum diameter less than about 0.00005 4. Atomized pellets consisting essentially of from 0.5 to 20% by volume of solid insoluble particles of magnesium intermetallic compound and the balance magnesium-base alloy; said particles of magnesium intermetallic compound being intimately and uniformly dispersed throughout said magnesium-base alloy; said particles of magnesium intermetallic compound having a maximum diameter of 0.0001 inch; said magnesium intermetallic compound being formed of magnesium and a constituent, said constituent having a solid solubility in magnesium of less than 0.1 atomic percent; said atomized pellets comprising at least 70% of magnesium; and said atomized pellets having diameters smaller than about 10 mesh.

5. Atomized pellets consisting essentially of from 0.5 to 20% by volume of solid insoluble particles of magnesium intermetallic compound and the balance magnesium; said particles of magnesium intermetallic compound being intimately and uniformly dispersed through said magnesium; said particles or" magnesium intermetallic compound having a maximum diameter of 0.0001 inch; said magnesium intermetallic compound being formed of magnesium and a constituent, said constituent having a solid solubility in magnesium of less than 0.1 atomic percent; and said atomized pellets having diameters smaller than about 10 mesh.

6. Atomized pellets consisting essentially of from 0.5 to 20% by volume of solid insoluble particles of magnesium intermetallic compound, and the balance magnesiumbase alloy containing at least one matrix strengthening alloying constituent selected from the group consisting of manganese, aluminum, zinc, silver, bismuth, calcium, lithium, tin, zirconium, thorium and rare earth metal; said particles of magnesium intermetallic compound being intimately and uniformly dispersed throughout said magnesium-base alloy; said particles of magnesium intermetallic compound having a maximum diameter of 0.0001 inch; said magnesium intermetallic compound being formed of magnesium and a constituent, said constituent having a solid solubility in magnesium of less than 0.1 atomic percent; said atomized pellets comprising at least 70% of magnesium; and said atomized pellets having diameters smaller than about 10 mesh.

7. Atomized pellets consisting essentially of from 0.5 to 20% by volume of said insoluble particles of magnesium-silicon intermetallic compound and the balance magnesium-base alloy; said particles of magnesium-silicon intermetallic compound being intimately and uniformly dispersed throughout said magnesium-base alloy; said particles of magnesium-silicon intermetallic compound having a maximum diameter of 0.0001 inch; said atomized pellets comprising at least 70% of magnesium; and said atomized pellets having diameters smaller than about 10 mesh.

References (Jited in the file of this patent UNITED STATES PATENTS Leontis et al Nov. 17, 1953 

2. ATOMIZED PELLETS COMPRISING FROM 0.5 TO 20% BY VOLUME OF SOLID INSOLUBLE PARTICLES OF MAGNESIUM INTERMETALLIC COMPOUND AND THE BALANCE MAGNESIUM-BASE ALLOY; SAID PARTICLES OF MAGNESIUM INTERMETALLIC COMPOUND BEING INTIMATELY AND UNIFORMLY DISPERSED THROUGHOUT SAID MAGNESIUM-BASE ALLOY; SAID PARTICLES OF MAGNESIUM INTERMETALLIC COMPOUND HAVING A MAXIMUM DIAMETER OF 0.0001 INCH; SAID MAGNESIUM INTERMETALLIC COMPOUND BEING FORMED BY MAGNESIUM WITH AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF BARIUM, COBALT, COPPER, GERMANIUM, ANTIMONY, NICKEL, SILICON, STRONTIUM AND MIXTURES THEREOF; AND SAID ATOMIZED PELLETS HAVING DIAMETERS SMALLER THAN ABOUT 10 MESH. 